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OWNER’S MANUAL
TEMPERATURE SENSORS
Models ST-100, ST-110, ST-200, and ST-300
APOGEE INSTRUMENTS, INC. | 721 WEST 1800 NORTH, LOGAN, UTAH 84321, USA
TEL: (435) 792-4700 | FAX: (435) 787-8268 | WEB: APOGEEINSTRUMENTS.COM
Copyright © 2016 Apogee Instruments, Inc.
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TABLE OF CONTENTS
Owner’s Manual .............................................................................................................................................................1
Certificate of Compliance .......................................................................................................................................3
Introduction ............................................................................................................................................................4
Sensor Models .......................................................................................................................................................5
Specifications .........................................................................................................................................................6
Deployment and Installation ...................................................................................................................................7
Operation and Measurement..................................................................................................................................8
Maintenance and Recalibration ............................................................................................................................ 11
Troubleshooting and Customer Support .............................................................................................................. 12
Return and Warranty Policy ................................................................................................................................. 14
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CERTIFICATE OF COMPLIANCE
EU Declaration of Conformity
This declaration of conformity is issued under the sole responsibility of the manufacturer:
Apogee Instruments, Inc.
721 W 1800 N
Logan, Utah 84321
USA
for the following product(s):
Models: ST-100, ST-110, ST-200, ST-300
Type: Temperature Sensor
The object of the declaration described above is in conformity with the relevant Union harmonization legislation:
2014/30/EU
2011/65/EU
Electromagnetic Compatibility (EMC) Directive
Restriction of Hazardous Substances (RoHS 2) Directive
Standards referenced during compliance assessment:
EN 61326-1:2013 Electrical equipment for measurement, control and laboratory use – EMC requirements
EN 50581:2012 Technical documentation for the assessment of electrical and electronic products with respect to
the restriction of hazardous substances
Please be advised that based on the information available to us from our raw material suppliers, the products
manufactured by us do not contain, as intentional additives, any of the restricted materials including cadmium,
hexavalent chromium, lead, mercury, polybrominated biphenyls (PBB), polybrominated diphenyls (PBDE).
Further note that Apogee Instruments does not specifically run any analysis on our raw materials or end products for
the presence of these substances, but rely on the information provided to us by our material suppliers.
Signed for and on behalf of:
Apogee Instruments, May 2016
Bruce Bugbee
President
Apogee Instruments, Inc.
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INTRODUCTION
Temperature is generally thought of as the relative degree of ‘hotness’ or ‘coldness’ of a specific object or material. In
actuality, temperature is a measure of the average thermal energy (internal kinetic energy) of an object. Thermal
energy is associated with the motion (kinetic energy) of the atoms and molecules making up the object/material.
Higher temperatures correspond to higher thermal energies (faster motion of atoms and molecules), whereas colder
temperatures correspond to lower thermal energies (slower motion of atoms and molecules).
Properties of materials and nearly all biological, chemical, and physical processes are temperature dependent.
Temperature is also a fundamental weather variable. As a result, temperature is perhaps the most widely measured
environmental variable.
Thermometers are sensors that measure temperature. Thermometers are often electronic, with multiple options
available. The main advantages of thermistors over other electronic thermometers (thermocouples, platinum
resistance thermometers) are high signal-to-noise ratio, requirement of only a single-ended channel for
measurement, and low cost, while still maintaining comparable accuracy.
Apogee Instruments ST-100 temperature sensors consist of a precision thermistor enclosed in a waterproof rubber
covering, a precision bridge resistor, and lead wires to connect the sensor to a measurement device. ST-100 sensors
are weatherproof and are designed for continuous temperature measurement in air, soil, or water.
ST-110 temperature sensors consist of a precision thermistor, a precision bridge resistor, and lead wires to connect
the sensor to a measurement device. ST-110 sensors are weatherproof, have excellent long-term stability, but do not
offer the same level of ingress protection as the ST-100. The ST-110 is designed for continuous air temperature
measurement when housed in the TS-100 aspirated radiation shield. Thermal conductivity to the precision thermistor
is minimized by using constantan wire, which has twenty-fold lower thermal conductivity than copper wire.
ST-200 temperature sensors have a fine-wire precision thermistor, precision bridge resistor, and lead wires, but the
thermistor is not packaged in a weatherproof housing. ST-200 sensors are weather resistant and are designed for
temperature measurement of delicate surfaces (e.g., leaves, fruits) and small samples (where a narrow field of view
infrared radiometer may not be suitable due to the integration over the conical field of view), or applications where
rapid response is required.
All Apogee thermistor temperature sensors output an analog voltage (when supplied with an input voltage) that is
related to thermistor resistance. Resistance is directly related to temperature.
ST-300 is a platinum resistance thermometer (PRT), consisting of a platinum resistive element enclosed in a
stainless steel sheath, and lead wires to connect the sensor to a measurement device. ST-300 sensor are
weatherproof and is designed for continuous air temperature measurement when housed in the TS-100 aspirated
radiation shield.
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SENSOR MODELS
The ST-100 temperature sensor includes a rugged, weatherproof housing and can be exposed
to a wide range of environmental conditions, including submersion in water and burial in
soil/porous media.
The ST-200 temperature sensor do not include the weatherproof housing and is designed for
fast response measurements, or measurements of small samples and fragile surfaces.
The ST-110 thermistor temperature sensor is designed for use inside the Apogee fanaspirated radiation shield, model TS-100.
The ST-300 PRT temperature sensor is a highly accurate and durable sensor for use in all
applications, including for air temperature measurements in the TS-100.
Sensor model number, serial number, and production
date are located on a label near the pigtail lead wires.
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SPECIFICATIONS
ST-100
ST-110
Measurement Range
Measurement Uncertainty
Measurement
Repeatability
Long-term Drift
(Non-stability)
Equilibration Time
Self-Heating
Operating Environment
Input Voltage
Requirement
Output Voltage Range
Current Drain
Dimension
ST-200
ST-300
-50 to 70 C
0.1 C (from 0 to 70
C), 0.2 C (from -25 to
0 C), 0.4 C (from -50
to -25 C)
0.1 C (from 0 to 70
C), 0.15 C (from -35
to 0 C)
0.2 C (from 0 to 70
C), 0.4 C (from -50 to
0 C)
0.1 C (from -40 to 60
C)
less than 0.05 C
less than 0.01 C
less than 0.05 C
less than 0.01 C
less than 0.05 C per
less than 0.02 C per year
year
(when used in non-condensing environments where the annual average temperature is less than
30 C; continuously high temperatures or continuously humid environments increase drift rate)
30 s
4s
1s
15 s
less than 0.01 C
(typical, assuming
pulsed excitation of
less than 0.01 C (typical, assuming pulsed excitation of 2.5 V DC; 0.08 C
2.1 V DC; 0.09 C at 5
at 5 C (maximum, assuming continuous input excitation of 2.5 V DC)
C (maximum,
assuming continuous
input excitation of 2.1
V DC)
-50 to 70 C; 0 to 100 % relative humidity
2.5 V DC excitation (recommended, see OPERATION AND
2.1 V DC
MEASUREMENT section)
16 to 27 mV DC
(assuming input
0 to 2.5 V DC ( assuming input excitation of 2.5 V DCC
excitation of 2.1 V
DC)
0.21 mA DC
(maximum, assuming
0.1 mA DC at 70 C (maximum, assuming continuous input excitation of
continuous input
2.5 V DC)
excitation of 2.1 V
DC)
100 mm length, 6 mm
diameter
80 mm length, 4 mm
diameter
25 mm length, 1 mm
diameter
Mass
60 g
Cable
5 m of two conductor, shielded, twisted-pair wire; additional cable
available in multiples of 5 m; santoprene rubber jacket (high water
resistance, high UV stability, flexibility in cold conditions); pigtail lead
wires
65 mm length, 3 mm
diameter
95 g
5 m of four
conductor, shielded,
twisted-pair wire;
additional cable
available in multiples
of 5 m; santoprene
rubber jacket (high
water resistance, high
UV stability, flexibility
in cold conditions);
pigtail lead wires
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DEPLOYMENT AND INSTALLATION
Apogee ST Series temperature sensors are designed to be mounted inside solar radiation shields, such as the model
TS-100 fan aspirated radiation shield (see picture below). ST-100 and ST-300 sensors can also be buried in
soil/porous media, or submerged in water. ST-200 sensors have thin, flexible wires near the fine-wire thermistor and
are less sensitive to breakage than similarly-sized fine-wire thermocouples.
The temperature measurement returned by a temperature sensor is the temperature for the sensor itself and not that
of the environment the sensor is in, unless the sensor is in thermal equilibrium with the environment. In order to get
representative temperature measurements, ST series sensors must be in thermal contact with the medium of interest.
Accurate air temperature measurement requires a radiation shield (see picture below) to minimize the effects of
shortwave radiation absorption (causes warming; occurs during the day) and longwave radiation emission (causes
cooling; occurs on clear nights) by the sensor. Proper ventilation is also required to ensure coupling and thermal
equilibrium with air. Condensation on air temperature sensors can pose a problem because it is a source of latent
heat that can warm the sensor. When the condensed water evaporates, it cools the sensor via removal of latent heat
(evaporational cooling).
During installation of ST-100 and ST-300 sensors in soil, care should be taken to minimize soil disturbance, which
may potentially alter soil thermal properties.
Top left: SP-230 Heated Pyranometer
Center: TS-100 Fan Aspirated Radiation Shield
Right: RM Young 41303 Static Solar Radiation Shield.
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OPERATION AND MEASUREMENT
ST-100, ST-110, and ST-200
Connect the sensor to a measurement device (meter, datalogger, controller) capable of inputting 2.5 V DC, and
measuring and displaying or recording a millivolt (mV) signal (an input measurement range of 0 to 2500 mV is
required to cover the entire temperature range of the sensor). In order to maximize measurement resolution and
signal-to-noise ratio, the input range of the measurement device should closely match the output range of the
thermistor.
Red: Excitation Channel (excitation for
thermistor)
Black: Single-Ended Channel (positive
thermistor lead)
Blue: Analog Ground (negative thermistor
lead)
Clear: Ground (shield wire)
Measurement devices (e.g., datalogger, controller) do not measure resistance directly, but determine resistance from
a half-bridge measurement, where an excitation voltage is input across the thermistor and an output voltage is
measured across the bridge resistor.
An excitation voltage of 2.5 V DC is recommended to minimize self-heating and current drain, while still maintaining
adequate measurement sensitivity (mV output from thermistor per C). However, other excitation voltages can be
used. Decreasing the excitation voltage will decrease self-heating and current drain, but will also decrease thermistor
measurement sensitivity. Increasing the excitation voltage will increase thermistor measurement sensitivity, but will
also increase self-heating and current drain.
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Conversion of Thermistor Resistance to Temperature
The thermistor is a resistive element, where resistance changes with temperature. Thermistor resistance (R T, in Ω) is
measured with a half-bridge measurement, requiring a known excitation voltage input (V EX) and a measurement of
output voltage (VOUT):
 V

R T  24900  EX  1
V
 OUT

(1)
where 24900 is the resistance of the bridge resistor in Ω. From resistance, temperature (TK, in Kelvin) is calculated
with the Steinhart-Hart equation and thermistor specific coefficients:
TK 
1
A  B ln( R T )  C(ln( R T )) 3
(2)
where A = 1.129241 x 10-3, B = 2.341077 x 10-4, and C = 8.775468 x 10-8 (Steinhart-Hart coefficients).
If desired, measured temperature in Kelvin can be converted to Celsius (TC):
TC  TK  273 .15 .
(3)
ST-300
Connect the sensor to a measurement device (meter, datalogger, controller) capable of inputting 2.1 V DC, and
measuring and displaying or recording a millivolt (mV) signal (an input measurement range of 16 to 27 mV is required
to cover the entire temperature range of the sensor). In order to maximize measurement resolution and signal-tonoise ratio, the input range of the measurement device should closely match the output range of the thermistor.
Red: High Side of Differential Channel 2
Black: Low Side of Differential Channel 2
Blue: High Side of Differential Channel 1
Clear: Ground (shield wire)
White: Analog Ground
Green: Low Side of Differential Channel 1
Orange: PRT Excitation Channel
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Measurement of PRT resistance is very similar to measurement of thermistor resistance, where a half-bridge
measurement is used. An excitation voltage is input across the bridge resistor and an output voltage is measured
across the PRT.
An excitation voltage of 2.1 V DC is recommended to minimize current drain, while still maintaining an adequate
voltage signal. However, other excitation voltages can be used. Decreasing the excitation voltage will decrease
current drain, but will also decrease output voltage. Increasing the excitation voltage will increase output voltage, but
will also increase current drain.
Conversion of PRT Resistance to Temperature
The PRT is a resistive element, where resistance changes with temperature. PRT resistance (R PRT, in Ω) is measured
with a half-bridge measurement, requiring a known excitation voltage input (VEX) and a measurement of output
voltage (VOUT):
R PRT  100 
VPRT
(1)
V100 
where 100 Ω is resistance of the bridge resistor, V100Ω is the voltage measured across the 100 Ω bridge resistor, and
VPRT is the voltage measured across the PRT. From resistance, temperature (TC, in Celsius) is calculated with:
A
TC 
R


A 2  4 B 1  PRT 
100 

2B
(2)
where A = 3.9083 x 10-3, B = 5.7750 x 10-7, and C = 4.1830 x 10-12.
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MAINTENANCE AND RECALIBRATION
Apogee ST-100 temperature sensors are weatherproof and can be submerged in water or buried in soil/porous
media. ST-110 sensors are weatherproof and designed for air temperature measurements inside radiation shields.
ST-200 series sensors are weather resistant, but not weatherproof. When sensors are not in use, it is recommended
that they be removed from the measurement environment, cleaned, and stored. ST series temperature sensors used
to measure air temperature should be periodically cleaned to remove all dust and debris.
Apogee ST-100, ST-110, and ST-200 temperature sensors are not factory calibrated, but come with a generic
calibration (see Steinhart-Hart coefficients in OPERATION AND MEASUREMENT section). A custom calibration can
be derived by comparing the temperature from the thermistor to a reference temperature measurement. Often, a
simple offset can be used to make measured temperature match reference temperature.
Apogee ST-110 and ST-300 temperature sensors are factory verified to ensure accuracy. Sensors are compared for
absolute temperature against the mean of two reference PRTs in a constant temperature bath, over a range of
approximately -35 to 60 C. The reference PRT calibrations are directly traceable to the NIST.
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TROUBLESHOOTING AND CUSTOMER SUPPORT
Independent Verification of Functionality
Apogee ST Series thermistor temperature sensors yield a resistance proportional to temperature. A quick and easy
check of thermistor functionality can be accomplished with an ohmmeter. Connect the lead wires of the ohmmeter to
the red and black wires from the sensor. The resistance should read 10 kΩ (10,000 ohms) at 25 C. If sensor
temperature is less than 25 C, resistance will be higher. If sensor temperature is greater than 25 C, resistance will be
lower. Connect the lead wires of the ohmmeter to the black and blue wires from the sensor. The resistance should
read 24.9 kΩ, and should not vary. Connect the lead wires of the ohmmeter to the red and blue wires from the
sensor. The resistance should be the sum of resistances measured across the red and black wires, and black and
blue wires (e.g., 10 kΩ plus 24.9 kΩ at 25 C).
Apogee ST-300 temperature sensors yield a resistance proportional to temperature. A quick and easy check of
sensor functionality can be accomplished with an ohmmeter. Connect the lead wires of the ohmmeter to the
white/black and red/green wires from the sensor. The resistance should read 100Ω (0.1 kΩ) at 0 C. If the sensor
temperature is less than 0 C, the resistance will be lower. If the sensor temperature is greater than 0 C, the
resistance will be higher. The white and black wires are connected internally, without a resistor between them;
continuity between white and black wires indicates both wires are functional. Similarly, the red and green wires are
connected internally, without a resistor between them; continuity between red and green wires indicates both wires
are functional. Connect the lead wires of the ohmmeter to the red/green and blue wires from the sensor. The
resistance should read 100 Ω, and should not vary. Connect the lead wires of the ohmmeter to the blue and orange
wires from the sensor. The resistance should read 10 kΩ, and should not vary. Connect the lead wires of the
ohmmeter to the white/black and orange wires from the sensor. The resistance should be the sum of the resistances
measured across the white/black and red/green wires wires, red/green and blue wires, and blue and orange wires
(e.g., 100 Ω plus 100 Ω plus 10 kΩ at 0 C).
Compatible Measurement Devices (Dataloggers/Controllers/Meters)
Measurement of thermistor resistance requires an input excitation voltage, where 2.5 V DC is recommended. A
compatible measurement device should have the capability to supply the necessary voltage.
The sensitivity (mV output from thermistor per C) of the temperature measurement varies with the excitation voltage,
and varies as a function of temperature. With an excitation voltage of 2.5 V DC, the sensitivity is lowest near the ends
of the measurement range, -50 and 70 C. A compatible measurement device (e.g., datalogger or controller) should
have resolution of at least 0.6 mV, in order to produce temperature resolution of less than 0.1 C across the entire
temperature measurement range (less than 0.05 C from -35 to 45 C).
The sensitivity (mV output from PRT per C) of the temperature measurement from the ST-300 PRT is approximately
constant across the entire measurement range. With an excitation voltage of 2.1 V DC, a compatible measurement
device should have resolution of at least 0.008 mV, in order to produce temperature resolution of less than 0.1 C
across the entire temperature measurement range.
An example datalogger program for Campbell Scientific dataloggers can be found on the Apogee webpage at
http://www.apogeeinstruments.com/content/Thermistor-Temperature-Sensor.CR1.
Modifying Cable Length
When the sensor is connected to a measurement device with high input impedance, sensor output signals are not
changed by splicing on additional cable in the field. Tests have shown that if the input impedance of the
measurements device is 1 mega-ohm or higher then there is negligible effect on ST series temperature sensors, even
after adding up to 100 m of cable. See Apogee webpage for details on how to extend sensor cable length
(http://www.apogeeinstruments.com/how-to-make-a-weatherproof-cable-splice/). For cable extensions, shielded,
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twisted pair cable is recommended, in order to minimize electromagnetic interference. This is particularly important
for long lead lengths in electromagnetically noisy environments.
The precision bridge resistor is located at the pigtail end of the cable. Thus, ST series temperature sensor cables
should not be shortened, otherwise the bridge resistor will be removed.
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RETURN AND WARRANTY POLICY
RETURN POLICY
Apogee Instruments will accept returns within 30 days of purchase as long as the product is in new condition (to be
determined by Apogee). Returns are subject to a 10 % restocking fee.
WARRANTY POLICY
What is Covered
All products manufactured by Apogee Instruments are warranted to be free from defects in materials and
craftsmanship for a period of four (4) years from the date of shipment from our factory. To be considered for warranty
coverage an item must be evaluated either at our factory or by an authorized distributor.
Products not manufactured by Apogee (spectroradiometers, chlorophyll content meters) are covered for a period of
one (1) year.
What is Not Covered
The customer is responsible for all costs associated with the removal, reinstallation, and shipping of suspected
warranty items to our factory.
The warranty does not cover equipment that has been damaged due to the following conditions:
1. Improper installation or abuse.
2. Operation of the instrument outside of its specified operating range.
3. Natural occurrences such as lightning, fire, etc.
4. Unauthorized modification.
5. Improper or unauthorized repair.
Please note that nominal accuracy drift is normal over time. Routine recalibration of sensors/meters is considered
part of proper maintenance and is not covered under warranty.
Who is Covered
This warranty covers the original purchaser of the product or other party who may own it during the warranty period.
What We Will Do
At no charge we will:
1. Either repair or replace (at our discretion) the item under warranty.
2. Ship the item back to the customer by the carrier of our choice.
Different or expedited shipping methods will be at the customer’s expense.
How To Return An Item
1. Please do not send any products back to Apogee Instruments until you have received a Return Merchandise
Authorization (RMA) number from our technical support department by calling (435) 792-4700 or by submitting an
online RMA form at www.apogeeinstruments.com/tech-support-recalibration-repairs/. We will use your RMA number
for tracking of the service item.
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2. Send all RMA sensors and meters back in the following condition: Clean the sensor’s exterior and cord. Do not
modify the sensors or wires, including splicing, cutting wire leads, etc. If a connector has been attached to the cable
end, please include the mating connector – otherwise the sensor connector will be removed in order to complete the
repair/recalibration.
3. Please write the RMA number on the outside of the shipping container.
4. Return the item with freight pre-paid and fully insured to our factory address shown below. We are not responsible
for any costs associated with the transportation of products across international borders.
5. Upon receipt, Apogee Instruments will determine the cause of failure. If the product is found to be defective in
terms of operation to the published specifications due to a failure of product materials or craftsmanship, Apogee
Instruments will repair or replace the items free of charge. If it is determined that your product is not covered under
warranty, you will be informed and given an estimated repair/replacement cost.
Apogee Instruments, Inc.
721 West 1800 North Logan, UT
84321, USA
OTHER TERMS
The available remedy of defects under this warranty is for the repair or replacement of the original product, and
Apogee Instruments is not responsible for any direct, indirect, incidental, or consequential damages, including but not
limited to loss of income, loss of revenue, loss of profit, loss of wages, loss of time, loss of sales, accruement of debts
or expenses, injury to personal property, or injury to any person or any other type of damage or loss.
This limited warranty and any disputes arising out of or in connection with this limited warranty ("Disputes") shall be
governed by the laws of the State of Utah, USA, excluding conflicts of law principles and excluding the Convention for
the International Sale of Goods. The courts located in the State of Utah, USA, shall have exclusive jurisdiction over
any Disputes.
This limited warranty gives you specific legal rights, and you may also have other rights, which vary from state to
state and jurisdiction to jurisdiction, and which shall not be affected by this limited warranty. This warranty extends
only to you and cannot by transferred or assigned. If any provision of this limited warranty is unlawful, void or
unenforceable, that provision shall be deemed severable and shall not affect any remaining provisions. In case of any
inconsistency between the English and other versions of this limited warranty, the English version shall prevail.
This warranty cannot be changed, assumed, or amended by any other person or agreement.
APOGEE INSTRUMENTS, INC. | 721 WEST 1800 NORTH, LOGAN, UTAH 84321, USA
TEL: (435) 792-4700 | FAX: (435) 787-8268 WEB: APOGEEINSTRUMENTS.COM
Copyright © 2016 Apogee Instruments, Inc.